Linear encoders for measuring mechanical displacements between an object and another object in linear directions (for example, a relativistic travel distance of an object in relation to another object), and rotary encoders for measuring mechanical displacements in rotational directions (for example, a rotational angle of an object relative to another object) are known. Patent Literature 1, Unexamined Japanese Patent Application Kokai Publication No. 2010-249602, discloses an optical encoder that measures a mechanical displacement between two objects by reading out a graduation mark on a scale provided on an object by using a readhead provided on another object.
In reference to optical encoders, a gap distance between a scale and a readhead needs to be maintained within a specified allowable limit of error (hereinafter, within “the tolerance”) due to properties of the optical encoders. However, the gap may occasionally be found outside of the specified tolerance due to deformations in attachment portions of the scale and of the readhead; the deformations caused by heat, a physical shock, aging or the like. Hence, precision and accuracy of measurements in the optical encoders drop substantially so that a normal course of operations for encoder embodied products would be unattainable.
The present invention has been made in view of these problems, and it is an object of the present invention to provide a readhead control mechanism including an encoder capable of maintaining a high measurement precision and accuracy of an encoder, and an optical encoder.